As an optical device for realizing optical fiber communication at high speed of 100 Gb/s and large capacity, a dual polarization-quadrature phase shift keying (DP-QPSK) modulator has been known. For example, in the DP-QPSK disclosed in Patent Literature No. 1, two Mach-Zehnder type optical waveguides are provided on the LN substrate, and light beams output from the Mach-Zehnder type optical waveguides are polarization-combined and output by being combined in a relationship in which the planes of polarization of the light beams orthogonally intersect each other by rotating the plane of polarization of one or both of the light beams output from the Mach-Zehnder type optical waveguides. For the optical system configuration of polarization combination, for example, Patent Literature No. 2 discloses a configuration in which one of the planes of polarization is rotated by the ½ wavelength plate after performing collimation (condensing) using a lens (condensing element) disposed near the substrate output end and the obtained light beams are output after being combined by a mirror and a polarization beam splitter (PBS). The light beams modulated by the two Mach-Zehnder type optical waveguides form signals of four values. Therefore, by combining these in a polarization combining element, it is possible to obtain a polarization-multiplexed light output of eight values.
However, in these configurations, since space or man-hours for adjustment or arrangement of each optical system is required, there is a problem in terms of the size of a modulator or members cost and assembly cost. In order to solve this problem, as a condensing element mounted near the substrate output end in Patent Literature No. 2, for example, as disclosed in Patent Literature No. 3, the use of a lens array (condensing member) in which lenses, on which light beams output from two optical paths are incident and from which the light beams are output in parallel, are arranged and formed can be considered. By using the polarization combining element in which such a lens array, a mirror, and a PBS are made as one, improvements in modulator size reduction, members cost reduction, and productivity are expected.